This invention relates to apparatus for performing computed x-ray tomography.
In one method of computed tomography, a patient is supported for being translated along a longitudinal axis which is usually horizontally disposed. The axis coincides with the center of rotation of a rotatable base which has an x-ray source on one side of the center of rotation and a multiple array of x-ray detectors on the other side. A fan-shaped x-ray beam, that is thin in the longitudinal direction, is projected through the patient as the base rotates so that the detectors may develop signals indicative of x-ray transmission characteristics along a plurality of paths through a subject undergoing examination. Analog signals representative of x-ray attenuation by all of the volume elements in a layer of the body at various rotational angles are then converted to digital signals which are used by a computer to produce signals which may be used for controlling a cathode ray tube to display a reconstructed image of the layer. Further background information on computed tomography is obtainable in an article entitled "Image Reconstruction From Projections" by Gordon et al; Scientific American, Oct. 1975, Vol. 233, No. 4. A prior gantry appears in U.S. Pat. No. 3,922,522.
Another prior method of performing computed tomography involves jointly translating an x-ray source on one side of the body and a detector on the other side of the body across a body layer repeatedly and rotating the source and detector through a small angle for each translation.
In both of the foregoing examples, the x-ray beam is projected through a thin layer of the body so that the reconstructed layer is essentially perpendicular to the longitudinal axis along which the patient is translated to obtain views of successive layers. On some occasions, however, unique diagnostic information can only be obtained by viewing a slice or layer through the body which is tilted through a small vertical angle and is not perpendicular to the horizontal or longitudinal axis along which the patient is translated.